Frequency multiplier



Sept. 27, 1949.

I. J. F. GORDON 2,482,973

FREQUENCY MULTIPLIER Filed April so, 1946 OSCILLATOR ,-I2 v o v- II 35PULSE A4 A8 EidT? 34 20 R- F /l 1 VIDEO R. F. OUTPUT I5 I AMPLIFIER 7AMPLIFIER l 24 DELAY CIRCUIT Fig. 1

l0 OSCILLATOR 29 H PULSE II PULS I GROUPS FORMINEG V OUTPUT cIRcuI'rAMPLIFIER M V x22 Hg. 2 l5 DELAY CIRCUIT 40 BLOCKING I 42 CIRCUIT 38Jorhe F. Gordon Patented Sept. 27, 1949 FREQUENCY MULTIPLIER James F.Gordon, Towson, Md., assignor to Bendix Aviation Corporation, Towson,Md., a corporation of Delaware Application April 30, 1946, Serial No.665,957

9 Claims. (01. 250-36) This invention relates to frequency multipliersand more particularly to multipliers adapted to the multiplication ofnarrow pulses at a stable repetition rate.

This application has been divided and a divisional application bearingSerial No. 758,960 was filed July 3, 1947.

In previous practice the multiplication of frequencies has been subjectto various limitations and defects. Some methods are limited to doublingso that a large number of stages are needed to provide any extendedfactor of multiplication. When power requirements must be met by anamplifier used selectively as amplifier, doubler, or tripler, thenmethods of regulation must be added to provide the proper output for theselected condition of operation. In cases where power is not arequirement, other higher harmonics of an oscillator or amplifier may beselected and amplified, but then only of a somewhat limited order. Inany such situation where harmonic distortion, selection, andamplification are used, the problem of isolation of the desired harmonicfrom the many spurious oscillations and unwanted harmonics is not aneasy one nor is it usually favorably accomplished.

An object of this invention is to provide a means of frequencymultiplication in which the desired factor of multiplication may bereadily obtained without recourse to a large number of multiplyingchannels.

Another object of this invention is to provide a means of frequencymultiplication by which a large number of available frequencies arereadily selectable from one stable oscillator source.

A further object of this invention is to provide a means of frequencymultiplication in which unwanted harmonics and spurious oscillations arenot present to be amplified by the succeeding stage or stages.

Another object of this invention is to provide a means of frequencymultiplication in which selection of pre-set frequency is readilyaccomplished, both in calibration and operation, with a minimum ofadjustment and control devices.

. Still another object of this invention is to provide a means offrequency multiplication with an output of short pulses at a definiterepetition rate, and which means of multiplication effectively lendsitself to further control to provide an output of regular, successivegroups of two or more pulses.

Other objects and advantages of the invention will become apparent froma consideration of the following specification when taken in conjunctionwith the accompanying drawing, in which:

Fig. 1 is a block diagram showing a multiplying circuit embodying theinvention, in relation to its input, output, and tuning means; and,

Fig. 2 is a block diagram showing a modified form of the circuit of Fig.l in which the multiplier lends itself to the control of a blockingoscillator to provide an output of regular groups of pulses.

In Fig. l the output of an oscillator II] is connected by a lead I2 to apulse forming circuit I4 which combination supplies the pulse inputenergy required by the invention. The output of the pulse formingcircuit I4, is connected by a lead It to the input of a video amplifier20. The output of the amplifier 21! is fed by a lead 22 to a delaycircuit 24, and from said delay circuit by a lead 26 back to the inputof amplifier 20. Connected into the anode circuit of the amplifier 20 bytwo leads I8 is a current meter 30. Representing one use of thisinvention, the output from amplifier 20 is fed by connector 32 to driveand control a radio frequency amplifier 34, which is preferably a tuned,class C amplifier. The output tank circuit d2 of the amplifier 34comprises a coil 46 and a variable condenser 44, which may be ganged fortuning purposes with variable condensers 52 and 5a which control thedelay applied by the delay circuit 24. The ganging means is indicated bythe dashed line 5!).

In operation, the oscillator H), which is preferably crystal controlledfor stability, provides the fundamental operating frequency. To providethe pulsed output needed for the present means of frequencymultiplication, the fundamental oscillation frequency having a wave-formindicated by the graph i I is fed to the pulse forming circuit 14, theoutput of which consists of very narrow pulses as shown by graph l5,having a regular repetition rate established by the oscillator l0. Thesepulses are fed to the video amplifier 20 and subsequently multiplied ina manner now to be described.

If a very narrow pulse is fed to the video amplifier 2B, the amplifiedpulse will be fed to the delay circuit 24 and again to the input I3 ofsaid amplifier, where the delayed pulse will again be amplified and willfollow the initial pulse by an interval equal to the delay time of thedelay circuit 24. The second pulse will again be fed to the delaycircuit 20 and back to the input 18 of the amplifier 20 where it will beamplified and will follow the other two pulses by an interval 3 equal tothe delay interval between the first two pulses. Such action is startedby each pulse from the pulse forming circuit [4.

If the delay circuit 24 is set So that the delay time is 90 of thefrequency cycle time of the output of oscillator Ill, then three pulseswill follow the initial pulse through the video amplifier 58 before thearrival of the next pulse from the pulse forming circuit M. This pulsewill occur in step and identify itself with the fourth fedback pulsewhich is 360 behind the initial pulse to pass the amplifier 2c. Theoutput of amplifier. will now have a wave-form such as indicated by thegraph 33.

Under these conditions it can be seen that the output of said videoamplifier consists of four times as many pulses per second; as arepresent in the pulse source from the pulse forming circuit 14. If thedelay circuit 25 were set for a relay of 120 of the fundamentalfrequency cycle, then the pulse frequency at the output of the videoamplifier would be three times that of the initial frequency from thepulse formin circuit. If the delay \vere'set at 45, then the fre--quency at the output of the'video amplifier would be eight times theinitial frequency. Such multiplication could continue up to the limitsof the pulse width and the capabilities of thedelay circuit 24.

With a current meter 39 inserted. in the plate circuit of the videoamplifier 29, proper adjustment of the pulse delay interval can readilybe discerned by the occurrence-of a dip in the meter readin as the delayinterval becomes an integral sub-multiple of the original pulseinterval. the delay circuit were set for. a value of 95 delay instead ofa desired 99 behind the preceding pulse, the fourth pulse fed-back bythe delay circuit would not coincide with the next recurrent fundamentalfrequency pulse. In a short time, due to this discrepancy, the videoamplifier output would consist of a. great many random components all ofwhich would addworking time to the video amplifier. and would beindicated'by the meter because of added current. Should the delaycircuit be adjusted so that the delay time would be the desired 90-instead of 95, then the definite dip shown by the plate current meterwould indicate that the Video amplifier would be working the minimumtime of four pulses per fundamental frequency cycle.

With such a plate current indicatin device dips would occur with delaytime settings of 189, 12.0", 96, '72", 60, 45, or of any other delaytime union will constitute an integral submultiple of the pulse intervalof the output of the. pulse forming circuit 24. As stated above thepulse width and the capabilities of the delay. circuit provide a limitto frequency multiplication which may be attained.

In using a multiplier constructed. in accordance with this invention to.drive a class 03' radio frequency amplifier. such as 34; the anodecircuit of said F. amplifier is tuned'to a resonant frequency comparableto the repetition rate of the multiplied pulses driving its grid. Radiofrequency energy of controlled frequency is then available in the anodecircuit of the class C amplifier indicated by the graph The anode tuninof this amplifier 35 and the delay time adjustment of the delay circuit24. can be mechanically coupled as indicated at 58, to provide acontrolled output of a great number of multiples of. the frequency of"the sourceoscil lator 40.

iii)

The pulsed output of the multiplier can be used to provide precisionmarkers for a time base, since the oscillator H) can be very stable andthe delay conditions may be readily and accurately determined by use ofthe anode current meter 30.

The circuit illustrated in Fig. 2 differs from that of Fig.1 in that ablocking circuit 40 is inserted between the pulse formin circuit M andthe delay circuit 24. The output of the pulse forming circuit I4 is fedto the blocking circuit 4.0.: through lead 42 and the blocking circuitis connected to the delay circuit 24 by lead 38 in a manner to renderthe feed-back circuit, of which the delay circuit is a part, inoperativeduring the blocking interval. The blocking circuit may be any one of anumber of well known trigger circuits or synchronized multivibratorcircuits;

In the operation of the embodiment illustrated inv Fig. 2 the blockingcircuit 40 opcratestc render the feed-back circuit 22, 24, 23inoperative for acontrollable period of time during each pulse intervalof the output of the pulse formin circuiti i.4.. By this means pulsgroups of two or more pulses can be produced such as indicated by thegraph 3?. Variations of pulse groupingv can be obtained by propercontrol: of theoperating. interval of the blocking circuit 40;

It.- will. be. evident from the foregoing. that the invention is not.limited: to the specific circuits and arrangements of parts shown and.disclosed herein for illustration but that the underlying concept andprinciple of the invention are susceptiblev of numerous. variations. andmodificationseoining within the broader. scope and spirit thereof. asdefinedby the. appended. claims. The specification and. drawings areaccordingiy to be regarded in an; illustrative rather than a limitingsense;

What is. claimed is:

l. A frequency multiplying system comprising means. generating a uniformtrain of energy pulses;v means amplifying the output of saidgencratingmeans; means feeding back energy from the output of saidv amplifyingmeans to-the input thereof, saidfeed-back means comprising meansdelaying said energy. by an. integral sub-multiple ofthe-pulse intervalof said. train, an amplifying circuit connected to amplify the output ofsaid amplifying means, said amplifying circuit having a tuned outputcircuit resonant at the pulse repetition rate of said amplifying means;and ganged means for simultaneously tuning said resonant output circuitand varying the delay of said delay means, whereby said resonant outputcircuit is maintained tuned to the pulse repetition rate of saidamplifying means,

2; A frequency multiplying system in. accordance with claim 1; saidsystem comprising means for indicating when said delay means is delayingthe energy f d-back to the. input of said amplifying means by anintegral sub-multiple of the pulse interval of said train, saidindicating means comprising a current meter connected to measure theoutput current of said amplifying means, whereby a dip in the reading ofsaid meter indicates thatthe delay introduced by said delay means is anintegral fraction of said pulse interval.

3. A frequency multiplying system comprising means generating a uniformtrain of energy pulses; means amplifying the output of said generating.means; means feeding back energy from the outputiiofsaid amplifyingmeansto the-in put thereof, said feed-back means comprising meansdelaying said energy by an integral submultiple of the pulse interval ofsaid train; and an amplifying circuit connected to amplify the output ofsaid amplifying means, said amplifying circuit having a tuned outputcircuit resonant at the pulse repetition rate of said amplifying means.

4. A frequency multiplying system comprising means generating a uniformtrain of energy pulses; means amplifying the output of said generatingmeans, and means feeding back energy from the output of said amplifyingmeans to the input thereof, said feed-back means comprising meansdelaying said energy by an integral sub-multiple of the pulse intervalof said train.

5. A frequency multiplying system comprising means generating a uniformtrain of energy pulses; means amplifying the output of said generatingmeans, means fe'ding back energy from the output of said amplifyingmeans to the input thereof, said feed-back means comprising meansdelaying said energy by an integral submultiple of the pulse interval ofsaid train and means measuring the output current of said amplifyingmeans.

6. A frequency multiplying system comprising a stable pulse oscillator,a video amplifier connected to amplify the output thereof, a feedbackcircuit feeding energy from the output of said amplifier to the inputthereof, a delay circuit forming a part of said feed-back circuit andoperable to delay the energy fed-back thereby, by an integralsub-multiple of the pulse interval of said oscillator output, a currentmeter connected to indicate the output current of said amplifier, and atuned radio frequency amplifier connected to amplify the output of saidvideo amplifier.

7. A frequency multiplying system in accordance with claim 6, saidsystem comprising means for varying the delay interposed on saidfed-back energy by said delay circuit, means for varying the tuning ofsaid tuned amplifier and means connecting said delay varying means andsaid tuning means for simultaneous operation,

8. The method of multiplying the frequency of an energy wave whichcomprises forming said wave into a uniform train of energy pulses,amplifying said pulses, extracting energy from each of said pulses aftersaid amplification and inserting it into the portion of said train notyet amplified, said insertion being delayed by an integral sub-multipleof the pulse interval of said train, and converting said amplified traininto an oscillatory wave corresponding in frequency thereto.

9. The method of multiplying the frequency of an energy Wave whichcomprises forming said wave into a uniform train of energy pulses,amplifying said pulses, extracting energy from each of said pulses aftersaid amplification, inserting it after a delay into the portion of saidtrain not yet amplified, regulating said delay to an amount such that acondition of minimum current flow exists in said amplified train, andconverting said amplified train into an oscillatory Wave correspondingin frequency thereto.

JAMES F. GORDON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,442,781 Nichols Jan. 16, 19232,212,173 Wheeler Aug. 20, 1940 2,411,166 Olson Nov. 19, 1946 2,414,541Madsen Jan. 21, 1947 2,416,089 Jones Feb. 18, 1947 2,429,227 Herbst Oct,21, 1947

